nothing is not more permanent than the temporary

Wonder TempDB

Dubi Lebel

Dad, chef, gardener and

DBA

[email protected]

2

Who am I?

Dubi- Or Not To Be

To do is to be - Descartes

To be is to do - Voltaire

Do be do be do - Frank Sinatra

Yaba Daba Do - Fred Flintstone

11/2/2009 Dubi Or Not To Be

3

Temporary Agenda

It all about TemDB

For what?

Where?

How to?

best practice!


4

TempDB

Only one TempDB per instance.

Operations within TempDB are minimally logged.

data in TempDB does not persist after SQL Server shuts

down.

Only one file group in TempDB is allowed for data and

one file group for logs.

By default auto grow is enabled.

When the server restarts, the TempDB file size is reset

to the configured value (the default is 8 MB).


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What is TempDB

BOL:

The TempDB system database is a global resource that is

available to all users connected to the instance of SQL

Server and is used to hold the following:


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BOL: TempDB hold the following :

Temporary user objects that are explicitly

created, such as: global or local

temporary tables,

temporary stored procedures,

table variables,

Cursors (Key-set-driven and static cursors ).


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Internal objects that are created by the SQL Server

Database Engine, for example:

work tables to store intermediate results for:

spools

sorting.

Hash match.

Index (create with SORT_IN_TempDB )


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Row versions that are generated by data

modification transactions in a database that uses read-

committed

using row versioning isolation

snapshot isolation transactions.


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Row versions that are generated by data

modification transactions for features, such as:

online index operations,

Multiple Active Result Sets (MARS),

AFTER triggers.


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Is that all?


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TempDB also hold the following:

DBCC CHECK

Service Broker

Database Mail (Service Broker)

Event notifications (Service Broker)

Query notifications (Service Broker)

XML

Common table expression queries (with cte(col,col) as select..)

Large object (LOB) data type variables and parameters


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event log:

Source: MSSQLSERVER

Event ID: 17052

Description: The log file for database 'TempDB' is full.

Back up the transaction log for the database to free up

some log space


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error message

Server: Msg 8624, Level 16, State 1

Internal SQL Server error

or

Server: Msg 1101, Level 17, State 10, Line 1

Could not allocate new page for database 'TempDB'.

There are no more pages available in filegroup

DEFAULT. Space can be created by dropping objects,

adding additional files, or allowing file growth.


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How to plan TempDB Capacity ?

Check that auto-grow is on or off for TempDB

Execute individual queries , workload trace files , index

maintenance and monitor TempDB space.

Sum the space-use values from the previous steps to

predict your total workload usage.

adjust this value. And adjust again.


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How to Monitor TempDB Use?

sys.dm_db_file_space_usage - disk space that is used

sys.dm_db_session_space_usage and

sys.dm_db_task_space_usage - page allocation or

deallocation activity


http://msdn.microsoft.com/en-us/library/ms174412.aspx



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Monitoring TempDB Disk Space 1

SELECT

SUM(unallocated_extent_page_count) AS [free pages],

(SUM(unallocated_extent_page_count)*1.0/128) AS [free space in MB]

FROM sys.dm_db_file_space_usage;

returns the total number of free pages and total free space in megabytes (MB) available in all files in TempDB


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SELECT SUM(version_store_reserved_page_count)

AS [version store pages used],

(SUM(version_store_reserved_page_count)*1.0/128)

AS [version store space in MB]


returns the total number of pages used by the version

store and the total space in MB used by the version store

in TempDB


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SELECT transaction_id

FROM

sys.dm_tran_active_snapshot_database_transactions

ORDER BY elapsed_time_seconds DESC;

If the version store is using a lot of space in TempDB, you

must determine what is the longest running transaction.


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SELECT SUM(internal_object_reserved_page_count)

AS [internal object pages used],

(SUM(internal_object_reserved_page_count)*1.0/128)

AS [internal object space in MB]


returns the total number of pages used by internal objects

and the total space in MB used by internal objects in

TempDB


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SELECT SUM(user_object_reserved_page_count)

AS [user object pages used],

(SUM(user_object_reserved_page_count)*1.0/128)

AS [user object space in MB]


returns the total number of pages used by user objects

and the total space used by user objects in TempDB.


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SELECT SUM(size)*1.0/128 AS [size in MB]

FROM TempDB.sys.database_files

returns the total amount of disk space used by all files

in TempDB.


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SELECT

SUM (user_object_reserved_page_count)*8 as usr_obj_kb,

SUM (internal_object_reserved_page_count)*8 as internal_obj_kb,

SUM (unallocated_extent_page_count)*8 as freespace_kb,

SUM (mixed_extent_page_count)*8 as mixedextent_kb

FROM sys.dm_db_file_space_usag


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which Transact-SQL statements are

the top consumers of tempdb space

SELECT t1.session_id, t1.request_id, t1.task_alloc, t1.task_dealloc, t2.sql_handle, t2.statement_start_offset, t2.statement_end_offset, t2.plan_handle FROM (Select session_id, request_id, SUM(internal_objects_alloc_page_count) AS task_alloc, SUM (internal_objects_dealloc_page_count) AS task_dealloc

FROM sys.dm_db_task_space_usageGROUP BY session_id, request_id) AS

t1, sys.dm_exec_requests AS t2 WHERE t1.session_id = t2.session_id AND (t1.request_id = t2.request_id)

ORDER BY t1.task_alloc DESC


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Perfmon counters

Access Methods::Worktables Created/sec

temporary objects and are used to store results for query

spool, LOB variables, and cursors.

Typically this number is < 200

Access Methods::Workfiles Created/sec

temporary results for hash joins and hash aggregates

Access Methods: Worktables From Cache Ratio


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Perfmon counters

Temp Tables Creation Rate (SQL Server 2005)

The number of temporary table or variables created/sec.

Temp Tables For Destruction (SQL Server 2005)

The number of temporary tables or variables waiting to be

destroyed by cleanup system thread.


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How to add space to TempDB?

ALTER DATABASE, the data file will return to the new

size every time you restart the instance of SQL Server.

Set the recovery model of TempDB to SIMPLE.

Turn on auto-grow, but be careful, % can be dangers!

based it on the speed of the I/O subsystem

BUT it is a good idea to turn off the auto-grow feature

for the TempDB data files













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Hardware

Generally, RAID 1+0 provides better write performance

than any other RAID level providing data protection,

including RAID 5.

Striping recommended

Separate from user databases

SQL Server 2008

CHECKSUM for new installs (Earlier versions – NONE, Not

changeable)

On upgrade NONE still default

Recommend setting CHECKSUM after upgrade


35

File Placement

On a high-performance IO subsystem

Preferably on a separate spindle(s)

IO subsystem requirements not as strict

Durability not required (KB917047)

RAM Disk or IO subsystem with cache

multiple files on the same physical spindle or multiple

devices?

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Number of Files

create as many files as needed to maximize disk

bandwidth.

One of the best practice is to create one data file for

each (virtual) CPU on the server

KB 328551 -

Trace flag 1118 switches allocations in TempDB from

single-page at a time for the first 8 pages

create the files with equal sizing


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equal sizing

The equal sizing of data files is critical because the

proportional fill algorithm is based on the size of the

files. If data files are created with unequal sizes, the

proportional fill algorithm tries to use the largest file

more for GAM allocations instead of spreading the

allocations between all the files, thereby defeating the

purpose of creating multiple data files.


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Moving TempDB from system disk

Alter database TempDB modify file

(name = tempdev,

filename = „DEV:\MyPath\TempDB.mdf')

Alter database TempDB modify file

(name = templog,

filename = „DEV:\MyPath\templog.ldf')

Restart server


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What about the log file?

Most operations in tempdb are not logged.

Operations on user objects are logged.

Sort operations in tempdb also require logging.

Estimating the log space:

similar to estimating the log file size for other databases.

Multi log files?


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Moving TempDB from system disk

Be careful when you move the TempDB database

because if the TempDB database cannot be created,

SQL Server will not start. If the TempDB database

cannot be created, start SQL Server by using the (-f)

startup parameter and move the TempDB database to a

valid location.


41

What about Shrinking files?

Auto shrink is not allowed for tempdb.

How to shrink the TempDB database in SQL Server

http://support.microsoft.com/kb/307487

It is not recommended!



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What about auto update stats?

disabling the auto update stats

Usually objects created in the TempDB are fairly small

and, as such, the statistics will not reach the threshold

that causes the statistics to update automatically.

However, you'll need to manually update statistics if you

occasionally use large temporary objects.

What about “auto create statistics”


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Indexing temporary table

Indexing temporary large temp tables greatly increases

TempDB performance

use the normal CREATE INDEX command after the table

has been created.

table variables cannot have indexes created on them.

But can have a primary key defined upon creation

using the DECLARE @variable TABLE command.


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Restrictions Adding filegroups.

Backing up or restoring the database.

Changing collation. The default collation is the server collation.

Changing the database owner. TempDB is owned by dbo.

Creating a database snapshot.

Dropping the database.

Dropping the guest user from the database.

Enabling change data capture.


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Restrictions

Participating in database mirroring.

Removing the primary filegroup, primary data file, or log file.

Renaming the database or primary filegroup.

Running DBCC CHECKALLOC.

Running DBCC CHECKCATALOG.

Setting the database to OFFLINE.

Setting the database or primary filegroup to READ_ONLY.


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Working with tempdb in SQL Server 2005

http://technet.microsoft.com/en-us/library/cc966545.aspx

Capacity Planning for TempDB


TempDB Database


Concurrency enhancements for the TempDB database


How to shrink the TempDB database in SQL Server














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END or AND ?

D.O.N.T.B


nothing is not more permanent than the temporary

Technology

monitor tempdb space

database tempdb

total space

tempdb bol

monitoring tempdb disk

tempdb use

tempdb capacity

internal object space